High performance two-ply friction material

ABSTRACT

The present invention relates to a two-ply fibrous base material comprising a more porous primary layer having elastic and oil absorbent characteristics bonded to a less porous secondary layer having high temperature resistance and high strength characteristics. The two-ply fibrous base material, when impregnated with a suitable resin, provides a friction material exhibiting good friction and wear characteristics and is especially useful in high energy end use applications.

This is a continuation-in-part of Ser. No. 08/784,415 filed Jan. 16,1997, now U.S. Pat. No. 5,775,468 issued Jul. 7, 1998.

TECHNICAL FIELD

This invention relates to a high performance two-ply fibrous basematerial. The fibrous base has a primary layer and a secondary layerwhich are joined together during a wet paper making process. The two-plyfibrous base material is useful in friction material applications.

The two-ply friction material of the present invention has increasedmechanical strength, thermal conductivity, dynamic friction, and wearresistant characteristics. The two-ply friction material of the presentinvention has higher durability and is less costly to produce thanconventional one-ply friction materials.

BACKGROUND ART

New and advanced transmission systems and braking systems are beingdeveloped by the automotive industry. These new systems often involvehigh energy requirements. Therefore, the friction materials technologymust be also developed to meet the increasing energy requirements ofthese advanced systems.

In particular, a new high energy type friction material is needed. Thenew high energy friction material must be able to withstand high speedswherein surface speeds are up to about 65 m/second. Also, the frictionmaterial must be able to withstand high facing lining pressures up toabout 1500 psi. It is also important that the friction material beuseful under limited lubrication conditions.

The friction material must be durable and have high heat resistance inorder to be useful in the advanced transmission and braking systems. Notonly must the friction material remain stable at high temperatures, itmust have excellent thermal conductivity, that is, the friction materialalso be able to rapidly dissipate the high heat that is being generatedduring operating conditions.

The high speeds generated during engagement and disengagement of the newtransmission and braking systems mean that a friction material must beable to maintain a relatively constant friction throughout theengagement. It is important that the frictional engagement be relativelyconstant over a wide range of speeds and temperatures in order tominimize “shuddering” of materials during braking or the transmissionsystem during power shift from one gear to another.

Previously, asbestos fibers were included in the friction material fortemperature stability. For example, the Arledter et al. U.S. Pat. No.3,270,846 patent describes phenolic and phenolic-modified resins usedwith asbestos. Now, however, due to health and environmental problems,asbestos is no longer being used. More recent friction materials haveattempted to overcome the absence of the asbestos in the frictionmaterial by modifying the impregnating paper or fiber materials withphenolic or phenolic-modified resins. These friction materials, however,do not rapidly dissipate the high heat generated, and do not have thenecessary heat resistance and satisfactory high coefficient of frictionperformance now needed for use in the high speed systems currently beingdeveloped.

Friction materials are often used in “wet” applications where thefriction material is “wetted” or impregnated with a liquid such as brakefluid or automatic transmission fluid during use. During use of the“wet” friction material, the fluid is ultimately squeezed from or isimpregnating the friction material. Wet friction materials differgreatly, both in their compositions and physical characteristics from“dry” friction materials.

In order for friction materials to be useful in “wet” applications, thefriction material must have a wide variety of acceptablecharacteristics. The friction material must be resilient or elastic yetresistant to compression set, abrasion and stress; have high heatresistance and be able to dissipate heat quickly; and, have longlasting, stable and consistent frictional performance. If any of thesecharacteristics are not met, optimum performance of the frictionmaterial is not met.

Thus, it is also important that a suitable friction lining or fibrousbase material be used to form a high energy application frictionmaterial. The friction material must have good shear strength both whensaturated with the wet resin during impregnation and when saturated withbrake fluid or transmission oil during use.

It is also important, under certain applications, that the frictionmaterial have high porosity such that there is a high fluid permeationcapacity during use. Thus, it is important that the friction materialnot only be porous, it must also be compressible. The fluids permeatedinto the friction material must be capable of being squeezed or releasedfrom the friction material quickly under the pressures applied duringoperation of the brake or transmission, yet the lining material must notcollapse. It is also important that the friction material have highthermal conductivity to also help rapidly dissipate the heat generatedduring operation of the brake or transmission.

Friction materials which met these demanding characteristics ofteninclude a fibrous base material having aramid-type fibers. However,these fibers and other ingredients used in the fibrous base material areexpensive which increases the cost of the friction material.

As far as is known, there is no disclosure of a friction material foruse in transmission systems which includes two-plies or layers offibrous base materials which have sufficient strength to be useful inhigh energy applications.

Accordingly, it is an object of the present invention to provide animproved friction material with reliable and improved propertiescompared to those of the prior art.

A further object of this invention is to provide friction materials withhigh thermal conductivity, porosity and strength.

As a result of extensive research in view of the need for a betterfriction material, a friction material with improved characteristics hasnow been developed.

DISCLOSURE OF THE INVENTION

In order to achieve the requirements discussed above, many materialswere evaluated for friction and heat resistant characteristics underconditions similar to those encountered during operation. Bothcommercially available brake linings and transmission materials wereinvestigated and proved not to be suitable for use in high energyapplications. The present invention is especially useful in brakes andin clutch applications. In one aspect, the present invention provides afibrous base material comprising two-plies or layers of material.

The two-ply fibrous base material comprises a primary or bottom layerand a secondary or top layer adjacent the first layer. The secondarylayer has a high temperature, high energy and low compression setformulation. The secondary layer comprises high temperature resistantand high strength fibers and friction paper-forming materials such as,for example, aramid fibers, carbon fibers, cotton or other cellulosefibers, fillers and/or phenolic or novoloid fibers and in certainembodiments, carbon particles and/or graphite particles. The first layeris more elastic and more oil absorbent that the second layer. Theprimary layer is highly porous, non-linearly elastic and has a lowcompression set. The primary layer comprises non-linearly elastic fiberssuch as aramid pulp and/or fibers, cotton fibers, and fillers, and incertain embodiments carbon particles and/or graphite particles.

Another aspect of the present invention relates to the two-ply fibrousbase material impregnated with at least one suitable resin for forming afriction material. The two-ply friction material is especially usefulfor friction materials for clutch friction plates, bands, synchronizerrings and related transmission friction products.

The fibrous base material can be impregnated using different resinsystems. In certain embodiments, it is useful to impregnate the fibrousbased material with a phenolic resin or a modified phenolic-based resin.It has now been discovered that, in certain embodiments, when a siliconeresin is blended or mixed with a phenolic resin in compatible solventsand that silicone-phenolic resin blend is used to impregnate a fibrousbase material of the present invention, a high energy friction materialis formed. Such high energy friction material has high frictionstability and high heat resistance.

The friction material of the present invention prevents uneven liningwear and therefore the formation of separator plate “hot spots” fromdeveloping during the useful life of the friction material. When thereis little uneven wear on the friction material, there is more likelihoodto maintain “steady state” of the clutch or brake components andtherefore, more consistent performance of the clutch and brake. Further,the friction material of the present invention shows good shear strengthsuch that the friction material resists delamination during use.

The layers of the two-ply fibrous base material are joined togetherduring a wet paper making process. The primary or bottom layer offriction material is formed by mixing together fibers, fillers and/orfriction particles to form a first layer or ply. The secondary or toplayer of friction material is formed by mixing together fibers, fillersand/or friction particles and by depositing this mixture on top of theprimary layer. The fibers in the primary layer interlock with the fibersin the secondary layer to provide optimum interface strength between thetwo plies of the fibrous base material. In certain embodiments, thesecondary layer can comprise up from about 2% to about 50% of the totalcombined two-ply fibrous base material thickness. In certain embodimentsthe secondary layer can have a composition where the phenolic ornovoloid fibers provide bond strength between the carbon fibers and thephenolic or modified phenolic resin which is used to impregnate thetwo-ply fibrous base material.

According to the present invention, the secondary layer containsingredients chosen to achieve the performance requirements of aparticular end-use application. The primary layer ingredients areselected such that they compliment the performance of the top layer.Proper selection of the combined secondary and primary layer ingredientsinfluences characteristics of the friction material. Such performancecharacteristics as durability, friction wear, lubricity, permeability,elasticity and other related performance characteristics are enhancedusing the two-ply material of the present invention.

The two-ply friction material of the present invention possessesphysical characteristics that are unattainable from a single-plyfriction material. The two-ply friction material of the presentinvention is then saturated with a resin chosen to enhance the frictioncharacteristics of the two-ply material. The two-ply material of thepresent invention has increased durability and high friction performancecompared to single-ply friction materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic diagram showing a method for forming atwo-ply friction material.

FIG. 2 is a cross-section taken along the line 2—2 in FIG. 1, generallyshowing a two-ply friction material.

FIG. 3 is a graph comparing the dynamic coefficient of friction as thenumber of cycles increases for comparative Sample 3 and Examples G andH.

FIG. 4 is a graph comparing the dynamic coefficient of friction as thenumber of cycles increases for comparative Samples 3, 4 and 5 andExample I.

FIG. 5 is a graph comparing the dynamic coefficient of friction as thenumber of cycles increases for comparative Sample 3 and Example I.

FIG. 6 is a graph comparing the static and dynamic coefficients offriction as the number of cycles increases for Example J.

FIG. 7 is a graph comparing the static and dynamic coefficients offriction as the number of cycles increases for Example K.

FIG. 8 is a graph comparing the static and dynamic coefficients offriction as the number of cycles increases for Example L.

FIG. 9 is a TGA graph showing the percent of weight loss as temperatureincrease, the change in the derivative weight (%/° C.), and the amountand percent of residue for Example N.

FIG. 10 is a graph showing the compression and permanent set for anoncompressed friction material comprising comparative example 8impregnated with a phenolic resin.

FIG. 11 is a graph showing the compression and permanent set for anoncompressed friction material comprising comparative example 9impregnated with a phenolic resin.

FIG. 12 is a graph showing the compression and permanent set for anoncompressed friction material comprising comparative example Oimpregnated with a phenolic resin.

FIG. 13 is a graph comparing the coefficient of friction as the numberof cycles increases for comparative example 8 and example O.

BEST MODE OF CARRYING OUT THE INVENTION

In one aspect of the present invention provides a two-ply fibrous basematerial. The fibrous base material has a primary layer of onecomposition and a secondary layer bonded to the primary layer having adifferent composition. The thickness and composition of each layer canvary as the end use application needs change. The two-ply fibrous basematerial contains ingredients which provide optimum results for the enduse friction applications. The secondary layer is adjacent the area ofcontact in a clutch or friction lining application. The use of thevarious ingredients in the secondary layer provides a cost efficientfriction material and allows the optimum use of such ingredients thatmay have otherwise been eliminated from formulations because of highcosts. Further, the secondary layer provides a structure that isespecially useful in high energy applications. It is furthersurprisingly found that the two-ply friction material has increasedfriction characteristics and decreased wear. Further, the two-plyfriction material is more durable than conventional friction materials.

In various embodiments of the present invention, the primary or bottomlayer comprises a composition comprising, for example, at least one typeof non-linearly elastic fiber such as high strength less fibrillatedaramid fiber, cotton fibers, at least one type of filler material suchas diatomaceous earth (celite), and in certain embodiments carbonparticles and/or graphite particles. The secondary or upper layer has acomposition which differs from the primary layer. The secondary layercomprises, for example, high temperature resistance and high strengthfibers such as fibrillated aramid fibers and carbon fibers; phenolic ornovoloid fibers; fillers and, in certain embodiments, carbon particlesand/or graphite particles and optionally cotton fibers. The ingredientsin the secondary layer provide optimum performance characteristics tothe friction material while lowering the costs of manufacturing thefriction material.

In other embodiments of the present invention, the primary layer andsecondary layer can comprise the same or different compositions, andhave different basis weights and/or densities. In especially preferredembodiments, the primary layer has a low density, while the secondarylayer has a high density. In such embodiments, the primary and secondarylayers can both comprise one or more types of fibers, fillers andfriction particles.

Various types of fibrous or raw pulp materials are useful in the primaryand/or secondary layers in the present invention. Partially usefulfibrous materials can comprise cotton fibers, glass fibers, carbonfibers and/or aramid polyamide fibers such as aramid floc pulp and/orfibers which are generally designated as aromatic polycarbonamidematerials.

It is to be understood that various paper formulations are useful in thepresent invention and that other fibrous materials can be present in thefibrous base material formulations. For example, cotton burns at arelatively low temperature of approximately 350° C. Therefore, afriction material has a range of expected thermal stability based on theingredients used in the fibrous base material during the paper formingprocess. The fibrous base materials which comprise relatively highpercentages of cotton fibers would be less thermally stable than fibrousbase materials containing more thermally stable ingredients such asaramid pulps. The range and percentages of such ingredients aredependent upon the end use of the friction material and whether suchfriction material is to be subjected to moderate energy requirements orhigh energy requirements.

Carbon fibers are useful in the secondary layer. The carbon fibersprovide temperature resistance to the friction material matrix. Thecarbon fibers increase wear resistance and lining compressionresistance. The carbon fibers also provide delamination resistance andnoise or Squeal resistance. When a friction lining material isexhibiting these two characteristics, there is an improvement in fluidcapillary flow through the friction material. The increase incompression resistance prevents or decreases the friction material'schance of collapsing such that the capillary flow is maintained andsometimes improved. In various embodiments, the carbon fibers can bepresent at a range of about 5% to about 30%, and preferably about 20%.

It has surprisingly been found that when non-linearly elastic fiberssuch as less fibrillated aramid fibers having about a 525-650 CSF,preferably about 625 CSF, on the Canadian Standard Freeness index areincluded in the primary layer, there is an improvement in the strengthof the fibrous base material. The less fibrillated aramid fibers alsoprovide the primary or bottom layer with an increased porosity such thatthe friction material readily absorbs and desorbs the oil or otherfluid.

It has also been surprisingly found that when more fibrillated aramidfibers having about a 250-525 CSF, preferably about 300 on the CanadianStandard Freeness index are included in the secondary or top layer, thetop layer is less porous than the primary or bottom layer. The morefibrillated aramid fibers generally have many fibrils attached to a corefiber material. The length of the fibrillated fiber ranges from about0.5 to about 6 mm. In certain embodiments, it is preferred to havefibers having a Canadian Standard Freeness ranging from about 150 toabout 450 and most preferably about 200-300. The “Canadian StandardFreeness” (T227 om-85) means that the degree of fibrillation of fiberscan be described as the measurement of freeness of the fibers. TheCanadian Standard Freeness test is an empirical procedure which gives anarbitrary measure of the rate at which suspension of three grams offibers in one liter of water may be drained. Therefore, the fibrillatedaramid fibers have a lower freeness or a lower rate of drainage thanother less fibrillated aramid fibers or pulp.

The more fibrillated aramid fibers in the fibrous base material act tohold or retain the filler material onto the surface of the fibrous basematerial.

The damping effect of the filler material which is held onto the surfaceof the fibrous base material by the fibrillated aramid fibers alsocauses the friction material to have better elastic properties. Ifvibration does occur, especially at low speeds, the friction material iselastic enough to absorb or dampen the vibrations and preventshuddering. The size of the filler material is preferred to be in therange of about 6 to about 38 microns in diameter and most preferablyhaving a mean diameter size of about 10 to about 15 microns and incertain embodiments, about 12 microns. It has been discovered that ifthe size is too large, the surface of the friction material is toorough. If the filler particle size is too small, then the fillermaterial become too densely packed in the fibrous base material and theresulting friction material is not sufficiently porous to quickly absorbthe automatic transmission fluid and effectively to dissipate heat.

The less fibrillated aramid fibers generally have few fibrils attachedto a core fiber. The use of the less fibrillated aramid fibers providesa friction material having a more porous structure; i.e., there are moreand larger pores than if a typical fibrillated aramid fiber is used. Theporous structure is generally defined by the pore size and liquidpermeability. In a preferred embodiment, the fibrous base materialdefines pores ranging in mean average size from about 2.0 to about 15microns in diameter. The length of the less fibrillated fiber rangesfrom about 0.5 to about 6 mm and has a Canadian Standard Freeness (CSF)of greater than about 450 and in certain embodiments, about 500 to about550 and in other certain embodiments, about 580-640 and most preferablyabout 620-640.

Therefore, the less fibrillated aramid fibers have higher freeness orhigher rate of drainage of fluid from the friction material than otheraramid fibers or pulp. Friction materials comprising the aramid fibershaving a CSF ranging from about 530-650, preferably about 580-640, andmost preferably about 620-640, provide superior friction performance andhave better material properties than friction materials containingconventionally more fibrillated aramid fibers. It has surprisingly beenfound that primary layers comprising less fibrillated aramid fibershaving the longer fiber length, together with the high Canadianfreeness, provide a friction material with high strength, high porosityand good wear resistance. High energy tests conducted with materialscontaining, for example, the less fibrillated aramid fibers (CSF about580-640), have good long-term durability and stable coefficients offriction.

The more porous the structure of the friction material, the moreefficient is the heat dissipation. The oil flow in and out of thefriction material during engagement of the friction material during useoccurs more rapidly when the friction material is porous.

The secondary or top layer also includes novoloid fibers which comprisea cross-linked phenol-formaldehyde polymer. In certain embodiments, ithas been found that a combination of novoloid fibers wherein one fibertype has a relatively shorter length with an average length of about 0.2mm and another fiber type has a relatively longer length with an averagelength of about 3 mm is especially useful. While not wishing to be heldto any one theory, it is believed that the relatively shorter fibers actmore like particles than like fibers and therefore act like a bindertype material in the friction material. The shorter particle-likenovoloid fibers provide an improved strength to the friction paper. Therelatively longer fibers, provides strength and structure to thefriction material by preventing collapse of the friction material whenthe friction material is under pressure. While not wishing to be held toany particular theory, it is believed that the novoloid fibers, whichare chemically similar to the phenolic resins which are present in thefriction material, bond to the phenolic resin material to help provideboth mechanical and chemical strength to the friction material. Invarious embodiments, the novoloid fibers can be present in the range ofabout 1 to about 10%, and preferably about 2%.

The use of graphite in the primary and/or secondary layers of thefibrous base material provides an oriented or three-dimensionalstructure to the fibrous base material. Graphite has a high thermalconductivity due to its three-dimensional structure, which, in turn,provides the friction material with the ability to dissipate heatrapidly.

In various embodiments, various types of suitable graphite arecontemplated as being useful with the present invention. For example,graphite can be made by graphitization of a raw stock material such aspetroleum coke and a coal tar pitch binder. The raw materials are mixedand heated to temperatures of about 2800 to about 3000° C. and specialgraphitizing furnaces which convert the baked carbon body into apolycrystalene graphite article. In certain embodiments, it is preferredthat the size and geometry of the graphite be in the range of about 20to about 50 m. In certain embodiments, it has been discovered that ifthe graphite particle is too large or too small, there is not theoptimum three-dimensional structure and consequently the heat resistantis not as optimum.

The primary and/or secondary layers of the fibrous base material caninclude carbon particles which have high thermal conductivity. Thecarbon particles provide the friction material with good heat conductionsuch that the friction material has desired heat resistance. The carbonparticles also provides the friction material with good frictioncharacteristics such as a good or smooth “feel” in shift and essentiallynoise or “squawk” free operation of the brakes and clutches. The carbonparticles are less structured and more randomly structured than graphiteparticles and are typically made by processing various substrates atrelatively lower temperatures (e.g., 1000° C.).

It is to be understood that various fillers are useful in both theprimary and secondary layers of the two-ply fibrous base material of thepresent invention. In particular, silica fillers such as diatomaceousearth (celite) and/or silica are especially useful. The celite is aninexpensive organic filler which bonds strongly to the fibrousmaterials. The strong bonds provide high mechanical strength to thefriction material. The celite also provides high coefficients offriction to the friction material. The celite also provides the frictionmaterial with a smooth friction surface and provides a good “shift feel”and friction characteristics to the friction material. However, it iscontemplated that other types of fillers are suitable for use in thepresent invention and the choice of filler depends upon the particularend use requirements of the two-ply friction material.

In certain embodiments, processing aids such as latex type materials,silicon nitride and other friction particles can be included in theprimary and/or secondary layers. When silicon nitride powder isincorporated into the fibrous base material formulation, there is animprovement in the dynamic coefficient of friction characteristics inthe resulting friction material. This is especially surprising sincefibers of silicon nitride are not suitable for inclusion in frictionmaterials due to their abrasiveness of the silicon nitride fibers to theclutch or brake parts. In preferred embodiments, the silicon nitrideparticles have an average diameter of size from about 0.5 to about 1.5microns. In certain embodiments, it has been found that silicon nitrideparticles having an average diameter size of about 1 micron workexceptionally well. One type of silicon nitride particles is availableas Si₃N₄. The silicone nitride particles increase the dynamiccoefficient of friction when used at low levels of about 3% to about15%. In various preferred embodiments, the silicone nitride compositioncan comprise from about 4% to about 6%.

It is to be understood that if the initial coefficient of friction islow, than a friction material does not achieve its desired constantcoefficient of friction value until after many uses or cycles of thefriction material. The present invention provides a two-ply frictionmaterial having a high initial coefficient of friction. Further, whenthe dynamic coefficient of friction is close to the static coefficientof friction, there is a smooth transfer from one gear to another in aclutch operation. The present invention achieves a surprisingly goodstatic-to-dynamic coefficient of friction ratio with the addition ofsilicon nitride particles in the friction material.

Other ingredients such as friction particles and processing aids areuseful in the fibrous base materials. These friction particleingredients include, for example, cashew nut shell liquid particlesand/or rubber-type or elastomeric polymer particles. In especiallypreferred embodiments, the elastomeric polymer particles comprise about70% to about 75% elastomeric material (such as isoprene and/or nitriderubber materials) with the balance being processing aids. Theelastomeric particles are useful to provide additional friction liningwear resistance. The rubber-type particles allow the friction materialsto conform more closely to the mating parts (such as separator platesand a clutch) and therefore provide an increase in “real” versus“apparent” areas of contact between the separator plates. The frictionparticles increase the energy capacity of the two-ply friction material.

The secondary layer of the two-ply fibrous base material can be formedfrom an aqueous slurry comprising about, by wt., based on the weight ofthe aqueous slurry formulation for the secondary layer of the fiber basematerial: from about 5 to about 30% carbon fibers, most preferably about10%; about 0 to about 30% cotton fibers; about 5 to about 45% morefibrillated aramid fibers having about a 525 CSF or less, mostpreferably about 43% fibers having about 300 CSF; about 0 to about 30%carbon particles and/or graphite, most preferably about 15% carbonparticles; about 5 to about 35% filler such as diatomaceous earth, mostpreferably 30%; about 1 to about 10% of novoloid fibers, most preferablyabout 2%; and, about 0 to about 3% latex processing aid, most preferablyabout 2%. It is to be understood, that in certain embodiments, thesecondary layer can be formed with both carbon particles and graphiteparticles, with either graphite or carbon particles, or with no carbonparticles or graphite particles.

The primary or bottom layer of the two-ply fiber base material can beformed from aqueous slurry comprising, about, by wt., based on theweight of the aqueous slurry formulation for the bottom or primary layerof the fiber base material: from about 20 to about 50% cotton fibers,most preferably about 40%; about 10 to 40% filler material, mostpreferably about 25%; about 5 to about 30% less fibrillated aramidfibers having a CSF of about 525 or greater, most preferably about 10%fibers having about 625 CSF; about 0 to about 30% graphite and/or carbonparticles, most preferably about 20% graphite; and, about 0 to about 3%latex processing aid, most preferably about 2%. It is to be understoodthat, in certain embodiments, the primary layer can be formed with bothgraphite particles and carbon particles, with either graphite particlesor carbon particles, or with no graphite particles or carbon particles.

In a preferred embodiment, the top or secondary layer is less porousthan the bottom or primary layer. The less porous top layer is comprisedof high strength materials such as aramid fibers, carbon particles,carbon fibers and novoloid fibers which also act to dissipate heat byconduction, due at least in part to the presence of the carbon fibersand carbon particles. The more porous bottom layer can be comprised ofless expensive, lower thermal conductivity ingredients which allow heatto dissipate by convection due to the flow of the fluids (for example,automatic transmission oil) into and out of the pores in the bottomlayer of the friction material. Therefore, the two-ply friction materialof the present invention takes advantage of both heat conduction andheat convection to rapidly remove heat from the friction material.

The ingredients which comprise the secondary or upper layer are mixedtogether to a substantially homogenous blend and are deposited on top ofthe primary layer. It is to be understood that various methods fordepositing the secondary layer on top of the primary layer can be madeaccording to the present invention.

The process for making the two-ply fibrous base material of the presentinvention comprises adding the ingredients of the primary or bottomlayer material to form a substantially homogeneous blend. A paper isformed into a fibrous base material from the homogenous blend.

FIG. 1 provides a schematic diagram of one method for forming a two-plyfibrous base material. A first dispensing means 10 supplies theingredients to form a primary or lower layer 12 of a two-ply fibrousbase material 24. The ingredients forming the primary layer 12 aresupplied onto a suitable surface 11 which holds or conveys the primarylayer 12. It is to be understood that various surfaces 11 can be usedwith the present invention. A second dispensing means 20 generallysupplies the ingredients to form a secondary or upper layer 22 on to theprimary layer 12 to form a two-ply material 24. It is to be understoodthat suitable dispensing means 10 and 20 can comprise a header box orroller means or other suitable apparatus to apply a generally uniformlayer of the primary layer 12 and the secondary layer 22 to form thetwo-ply material 24.

In various embodiments, it is contemplated that the ingredientscomprising the primary and/or the secondary layers can include asuitable resin material. In such embodiments, the two ply material 24 isdried by a suitable drying means 30 to remove excess moisture from thetwo ply material and/or to cure the resin that is present in the two plymaterial. In certain embodiments it is contemplated that the dryingmeans can comprise heat rolls or infrared heating means or suitableheating means. It is to be understood that in embodiments where theingredients comprising the primary and secondary layers do not contain aresin, the two ply fibrous base material can be formed and thensaturated or impregnated with a suitable resin or resin combination, asshown in phantom in FIG. 1, by a suitable impregnating means 40. Theimpregnated two ply material can then be dried by a further suitabledrying means 50 to remove excess moisture and/or cure the resin.

FIG. 2 generally shows a cross-section of the two-ply fibrous basematerial 24 comprised of the primary or lower layer 12 and the secondaryor upper layer 22. The embodiment shown in FIG. 2 is shown for purposesof general illustration. It is to be understood that the secondary layercan preferably comprise from about 2% to about 50% of the thickness ofthe two-ply fibrous base material. In preferred embodiments, thesecondary layer comprises from about 10% to about 50% of the thicknessof the material and in certain preferred embodiments, about 10 to abut20%.

It has been surprisingly found that the secondary layer sufficientlybonds to the primary layer, such that essentially no delaminationproblems occur during use of the two-ply material of the presentinvention.

The friction material of the present invention has adequate interfacialstrength and is readily bonded to a suitable substrate such as a clutchplate or used as a brake lining material.

According to the present invention, various types of resins are usefulto saturate the two-ply fibrous base material. The type of resin used tosaturate a fibrous base material can influence the performance of theresulting friction material. The degree of toughness that a resinexhibits may be reflected by the friction material being able tomaintain its integrity when tested. It is important that both thephysical and frictional characteristics of the friction material remainintact during the expected service period of the end use product. Afriction material impregnated with a brittle resin may crack under aheavy load which acts to collapse the open porous structure of thefriction material matrix. On the other hand, a friction materialimpregnated with an elastomeric resin would provide desired coefficientand torque, but may lack the wear resistance and strength required tohold the friction material matrix intact. Thus, an ideal resinformulation has high strength and is still flexible. A resin with hightoughness provides optimum friction performance.

Various resins useful in the present invention include phenolic resinsand phenolic-based resins. It is to be understood that variousphenolic-based resins which include in the resin blend other modifyingingredients, such as epoxy, butadiene, silicone, tung oil, benzene,cashew shell nut oil and the like, are contemplated as being useful withthe present invention. In the phenolic-modified resins, the phenolicresin is generally present at about 50% or greater by weight (excludingany solvents present) of the resin blend. However, it has been foundthat friction materials, in certain embodiments, can be improved whenthe impregnant resin blend contains about 5 to about 80%, by weight, andfor certain purposes, about 15 to about 55%, and in certain embodimentsabout 15 to about 25%, by weight, of silicone resin based on the weightof the silicone-phenolic mixture (excluding solvents and otherprocessing acids).

Silicone resins useful in the present invention include, for example,thermal curing silicone sealants and silicone rubbers. Various siliconeresins are useful with the present invention. One resin, in particular,comprises xylene and acetylacetone (2,4-pentanedione). The siliconeresin has a boiling point of about 362° F. (183° C.), vapor pressure at68° F. mm, Hg: 21, vapor density (air=1) of 4.8, negligible solubilityin water, specific gravity of about 1.09, percent volatile, by weight,5% evaporation rate (ether=1), less than 0.1, flash point about 149° F.(65° C.) using the Pensky-Martens method. It is to be understood thatother silicone resins can be utilized with the present invention. Otheruseful resin blends include, for example, a suitable phenolic resincomprises (% by wt.): about 55 to about 60% phenolic resin; about 20 toabout 25% ethyl alcohol; about 10 to about 14% phenol; about 3 to about4% methyl alcohol; about 0.3 to about 0.8% formaldehyde; and, about 10to about 20% water. Another suitable phenolic-based resin comprises (%by wt.): about 50 to about 55% phenol/formaldehyde resin; about 0.5%formaldehyde; about 11% phenol; about 30 to about 35% isopropanol; and,about 1 to about 5% water.

It has also been found that another useful resin is an epoxy modifiedphenolic resin which contains about 5 to about 25 percent, by weight,and preferably about 10 to about 15 percent, by weight, of an epoxycompound with the remainder (excluding solvents and other processingaids) phenolic resin. The epoxy-phenolic resin compound provides, incertain embodiments, higher heat resistance to the friction materialthan the phenolic resin alone.

It further contemplated that other ingredients and processing aids knownto be useful in both preparing resin blends and in preparingimpregnating fibrous-based materials can be included in the frictionmaterials.

In particular, for the embodiments where a phenolic resin and siliconeresin are used, no new compound is formed when the silicone resin andphenolic resin are blended together. The resins cure separately and nonew compound is formed.

Both the silicone resin and the phenolic resin are present in solventswhich are compatible to each other. These resins are mixed together (incertain preferred embodiments) to form a homogeneous blend and then usedto impregnate a fibrous base material. There is not the same effect if afibrous base material is impregnated with a phenolic resin and then asilicone resin is added thereafter or vice versa. There is also adifference between a mixture of a silicone-phenolic resin solution, andemulsions of silicone resin powder and/or phenolic resin powder. Whensilicone resins and phenolic resins are in solution they are not curedat all. In contrast, the powder particles of silicone resins andphenolic resins are partially cured. The partial cure of the siliconeresins and the phenolic resins inhibits a good impregnation of thefibrous base material.

The fibrous base material is impregnated with a blend of a siliconeresin in a solvent which is compatible with the phenolic resin and itssolvent. In one embodiment, isopropanol has been found to be anespecially suitable solvent. It is to be understood, however, thatvarious other suitable solvents, such as ethanol, methyl-ethyl ketone,butanol, isopropanol, toluene and the like, can be utilized in thepractice of this invention. The presence of a silicone resin, whenblended with a phenolic resin and used to impregnate a fibrous basematerial, causes the resulting friction materials to be more elasticthan fibrous base materials impregnated only with a phenolic resin. Whenpressures are applied to the silicone-phenolic resin blended impregnatedfriction material of the present invention, there is a more evendistribution of pressure which, in turn, reduces the likelihood ofuneven lining wear. After the silicone resin and phenolic resin aremixed together, the mixture is used to impregnate a fibrous basematerial.

Various methods for impregnating materials can be practiced with thepresent invention. The fibrous base material is impregnated with thephenolic or modified phenolic resin, preferably so that the impregnatingresin material comprises about 30 to about 65 parts, by weight, per 100parts, by weight, of the friction material. After the fibrous basematerial has been impregnated with the resin, the impregnated fibrousbase material is heated to a desired temperature for a predeterminedlength of time to form the friction material. The heating cures thephenolic resin at a temperature of about 300°-350° F. When other resinsare present, such as a silicone resin, the heating cures the siliconeresin at a temperature of about 400° F. Thereafter, the impregnated andcured friction material is adhered to the desired substrate by suitablemeans.

The following examples provide further evidence that the two-ply fibrousbase material and the two-ply friction material of the present inventionare an improvement over conventional friction materials. Variouspreferred embodiments of the invention are described in the followingexamples, which, however, are not intended to limit the scope of theinvention.

It is also to be understood that the type of lubricant used in a wetfriction environment affects the characteristics of the two-ply frictionmaterial. Lubricants influence the performance of variouscharacteristics of the resulting two-ply friction material, includingstatic friction, dynamic friction (and therefore static/dynamic ratio),viscosity, viscosity index, oxidation stability, extreme pressurecapability and the like. The interface between the two-ply frictionmaterial and the desired substrate and the mechanical and chemicalfactors effect the friction material's performance. The two-ply frictionmaterial of the present invention is useful with various lubricants. Theselection of the optimum ingredients and range of ingredients can bedetermined by evaluating conditions under which the friction materialwill be exposed and the type of lubricant materials to be used in suchsystem.

EXAMPLE I

Various compositions of two-ply fibrous base materials were formed andsaturated with a phenolic resin to about a 30%-35% pickup level andcured to form two-ply friction materials. The following materials wereused in Example I as shown in Table 1 below.

TABLE 1 All two-ply papers (Ex. A, B, C, D, E and F) have a primary orfirst layer of cotton 60% and celite 40%. Compar. 1 One-Ply of cotton60%, celite 40% Basis Wt. = 125, Caliper 0.019″ Ex. A Second-Ply ofaramid floc and/or fiber 5% Basis Wt. = 150, Caliper = 0.022″ Ex. BSecond-Ply of aramid floc and/or fiber 5% and silicon nitride - 1.2%Basic Wt. = 150, Caliper = 0.023″ Ex. C Second-Ply of aramid floc and/orfiber Pri. Layer Basis Wt. = 185-189, Sec. Layer Basis Wt. = 24-27,Total Basis Wt. = 212-217, Caliper = 0.030″ Ex. D Second-Ply of aramidfloc and/or fiber 90% and silicon nitride 10% Pri. Layer Basis Wt. =183-185, Sec. Layer Basis Wt. = 16-26, Total Basis Wt. 201-209, Caliper= 0.028″ Ex. E Second-Ply of Formulation #1: aramid floc and/or fiber30%, celite 25%, silica particles 20%, Friction particles: isoprene typeelastomeric particles 15%, and glass fibers 10% Pri. Layer Basis Wt. =148, Sec. Layer Basis Wt. = 32-40, Total Basis Wt. = 180-188, Caliper =0.025″ Ex. F Second-Ply of aramid floc and/or fibers 70% and carbonfibers 30% Pri. Layer Basis Wt. = 167-170, Sec. Layer Basis Wt. = 25-26,Total Basis Wt. = 193-195, Caliper = 0.028″ Compar. 2 One-Ply of cotton55%, aramid pulp 25%, celite 45%

In order to obtain information about the relative lubricant penetrationcharacteristics of a material, oil drop times were recorded. These timesgenerally reflect oil absorption characteristics of a material. Three orfour drops of Exxon 1975 Type “H” automatic transmission fluid were usedper plate for these tests.

The materials that performed poorly in the friction test discussed belowtended to have high oil drop times of about 200 seconds or more. Thesecond set of samples have a slightly higher oil drop time compared tothe first set of samples which indicates less lubricant flow into andthrough the assembly. The second set of samples were processed withdifferent fiber and particle formations. This improved secondary layerformation also slightly reduced oil flow into the assemblies. Thespecific oil drop times on selected materials are shown in Table 2below.

TABLE 2 Oil Drop Data Average No. of Time Std. Full Pack Material (sec.)Dev. Cycles * First Round Compar. 1 284.7 42.8 60 Ex. A 88.9 10.1 1050Ex. B 46.7 11.4 1050 Second Round Ex. C 114.1 26.5 1050 Ex. D 63.0 12.1400 Ex. E 198.2 38.9 69 Ex. F 96.4 9.9 300 * See Procedure 528A for testspecifications

The first set of test materials (Compar. 1, Ex. A and B) compares thedistribution of fibers and then a combination of fiber and particle. Thecontrol single-ply paper (Compar 1) consisted of only cotton and celite.These two ingredients were selected because of their oil absorptioncapabilities and economical benefit.

The Ex. A material utilized a cotton and celite base with aramid fiberas the top layer to concentrate this rather expensive fiber at the pointof contact. Advantages of using aramid fibers include an inherent highthermal resistance, a cost reduction per plate and providing an upperlayer of two-ply paper that has an open structure which allows oilretention.

Ex. B comprises fiber and particle combination to take advantage of thebenefits of aramid fibers mentioned above, plus the favorableperformance characteristics of silicon nitride which contributes to anincreased friction coefficient. The use of this ingredient in thesecondary layer application is especially appropriate due to itsrelatively high cost.

Low Velocity Friction Apparatus (LVFA) tests shown in Table 3 below wereperformed to evaluate and rank the frictional performance of the two-plymaterials. Ex. B performed with only a slight change of frictionmagnitude compared to Ex. A. The tests essentially revealed on variationin performance using the different materials. However, Ex. A and B didresult in slightly less lining wear than the Compar. 2 example.

TABLE 3 LVFA Data - 120 psi Exxon 1975 Lubrication Tumbled SteelSeparator Plates Lining Static Dynamic Wear Material Tested FrictionFriction mils Compar. 1 .102 .144 0.3 Ex. A .106 .147 0.2 Ex. B .101.144 0.4 Compar. 2 .103 .149 1.4

The data resulting from Full Pack testing indicates an improvedperformance associated with the use of two-ply friction materials thatcontain silicon nitride particles. Silicon nitride particle addition tothe secondary layer increases dynamic friction from 0.119 to 0.128, withno increase of lining wear. A summary of the full pack friction and wearresults are given below in Table 4 below.

TABLE 4 Full Pack Laboratory Data Exxon 1975 Lubrication DynamicFriction After Average Pack Materials 1050 Cycles Loss (mils) Compar. 1NA (stopped after 50 severe damage cycles) Ex. A .119 12.1 Ex. B .12812.3 Compar. 2 .117 10.0

LVFA tests were run to evaluate and rank the friction performance oftwo-ply materials. A summary of the friction and wear data is given inTable 5 below.

TABLE 5 LFVA Data - 120 psi Exxon 1975 Lubrication Tumbled Steel PlatesLining Static Dynamic Wear Material Tested Friction Friction mils Ex. C.108 .134 0.3 Ex. D .106 .139 0.5 Ex. E .096 .136 0.2 Ex. F .105 .1400.5 Compar. 2 .103 .149 1.4

The Ex. C and Ex. A (see Table 3) samples with a top layer of aramidfibers performed with coefficients dynamic of friction of 0.134 and0.147, respectively. The higher and more uniform concentration of aramidfibers as shown in Ex. C, provides a lower dynamic coefficient offriction than for the comparative Sample 2. Including silicon nitrideparticles to the secondary layer formulation slightly increased dynamicfriction from 0.134 to 0.139. Tests with silicon nitride and carbonfiber additions performed similarly. Lining wear was low for all of theExamples A, B, C, D, E and F papers.

In the Full Pack test shown in Table 6 below, the Ex. C ran the entire1050 cycles. All materials had wear.

TABLE 6 Full Pack Laboratory Data Exxon 1975 Lubrication DynamicFriction After Average Pack Materials Tested 1050 Cycles Loss (mils) Ex.C .123 37.8 Ex. D NA (0.112 after 400 31.6 cycles Ex. E NA (0.147 after50 severe damage cycles) Ex. F NA (0.130 after 300 71.3 cycles) Compar.2 .151 24.0

It is advantageous to use two-ply friction materials from a cost savingsperspective and as a tool for manufacturing customized papers. Thesaturated two-ply friction materials did not reveal any problems withseparation of layers. Two-ply friction materials provide a means forevaluating the friction and wear performance of specific ingredientslocated in the top layer.

The presence of silicon nitride increases the dynamic coefficient offriction with no increase in assembly wear. The LVFA data indicates thata top layer with formulation #1 performs with less lining wear and lowerfriction than Compar. 2 material.

EXAMPLE II

Example II shows that the two-ply friction material can be formed withtwo layers of different compositions which are joined together duringthe wet paper making process. It is found that the ingredients from eachlayer intertwine to form a two-ply fibrous base material havingsufficient interfacial strength for use as a friction material. Thefollowing examples were saturated with a phenolic resin as shown inTable 7 below.

TABLE 7 Ex. G First-Ply of cotton 10%, celite 40% Second-Ply ofFormulation #1 (40% Actual Pickup) Primary Basis Wt. = ^(˜)160,Secondary Basis Wt. = ^(˜)45, Total Basis Wt. = 193-196, Caliper =0.032″ Ex. H First-Ply of cotton 45%, celite 40%, glass fibers 15%Second-Ply of Formulation #1 (40% Actual Pickup) Primary Basis Wt. =^(˜)160, Secondary Basis Wt. = ^(˜)45, Total Basis Wt. = 190-201,Caliper = 0.033-0.035″ Ex. I First-Ply of cotton 60%, celite 40%Second-Ply of Formulation #1 (41% Actual Pickup) Primary Basis Wt. =^(˜)89, Secondary Basis Wt. = ^(˜)41, Total Basis Wt. = 130-140, Caliper= 0.0220-0.0235″ Compar. 3 Single-Ply of Formulation #1 (43% ActualPickup) Total Basis Wt. = 205-225, Caliper = 0.032-0.040″ Compar. 4Single-Ply of Formulation #1 (35% Actual Pickup) Total Basis Wt. = 135Compar. 5 Single-Ply of Formulation #1 (40% Actual Pickup) Total BasisWt. = 135

All test samples were saturated with a phenolic resin to a 40% pick-uplevel, except where noted. A friction and wear evaluation using aclutch-type assembly was conducted. Full Pack testing was performedaccording to procedures 528A or 428C. The 528A procedure does notspecify the recording of static friction values, according to the 45degree method defined in drawing #95407. Otherwise, the two full Packprocedures are identical.

Wet and dry tensile tests with raw paper in (a) machine, and (b)cross-machine directions were performed. The cross head speed was set at0.5 inches per minute, and chart speed to 1 inch per minute.

Capillary flow and liquid permeability tests were performed on thefriction material. These measurements reflect the ability of thefriction material to contain lubricant and transfer heat.

(A) TWO-PLY VERSUS SINGLE-PLY FRICTION MATERIAL

Dynamic Friction Evaluation (200 lb. basis weight).

Full Pack Tests #528

Similar friction and wear performance results from tests with single-plyand two-ply assemblies. The dynamic friction averaged about 0.14 after1050 cycles. Laboratory dynamic friction coefficients are listed inTable 8 below. Percent friction fade, between cycles 200 and 1050,averaged about 8% for all three materials tested. Ex. G which has cottonand celite in the lower layer, had the least percent of dynamicfrictional fade (5.3%). Assemblies with glass fibers added to thecotton, and celite lower layer (Ex. H), resulted in slightly higherfrictional fade (8.6%). The highest fade was measured with the Compar. 3sample (10.5%). FIG. 3 illustrates the change in dynamic friction as thenumber of cycles increase for Compar. 3, Ex. G and Ex. H.

Assembly Pack Wear (200 lb. Basis Weight)

Full Pack Tests #528

As seen in Table 8 below, assemblies with two-ply material had slightlyhigher lining wear. The Compar. 3, single-ply material, resulted in a+0.7 mils wear value. Wear of the two-ply papers with and without glassfibers (Ex. G and H) in the lower layer are 7.5 mils and 12.0 mils,respectively. Glass fibers in the lower layer stiffened the paper matrixslightly. The amount of friction material removal versus compression isundetermined. However, after testing the single-ply and two-plyassemblies have a similar physical appearance.

Appearance rankings of abrasion, breakout, glazing, and delamination aregiven in Table 9 below. All three friction materials were given aglazing ranking of “1.” Assemblies with Ex. H, which includes glassfibers in the lower layer, resulted in slightly higher surface abrasion.

TABLE 8 Full Pack Laboratory Data/1050 Cycle Procedure 528/PhenolicResin 40% P.U. Exxon 1975 AFT Clutch Assembly High Speed Average PeakMaterial Dynamic Loss-Mils Compar. 3 0.137 +0.7 Ex. G 0.144 12.0 Ex. H0.138  7.5 Compar. 4 0.135 Stopped @ Cycle 600 Compar. 5 0.133 Stopped @Cycle 550 Ex. I 0.131  9.0

TABLE 9 Lining Appearance Ranking 100 lb. Basis Wt./After 528 Full PackTest Clutch Assembly Material Abrasion Breakout Glazing DelaminationCompar. 3 0 0 1 0 Ex. E 0 0 1 0 Ex. H 1 0 1 0

(B) HIGH VERSUS LOW BASIS WEIGHT MATERIAL

Lower Basis Weight Paper (135 lb. basis weight)

As seen in Table 8 above, tests with a single-ply friction materials ata lower 135 lb. basis weight (Compar. 4 and Compar. 5), werediscontinued after 600 cycles of a test run according to the 528procedure. Lower basis weight paper at 35% and 40% resin pick-up levelswere stopped because of erratic friction coefficients. FIG. 4illustrates the friction versus number of cycles performance variationof 200 lb. and 135 lb. basis weight friction mate rials for Compar. 3,Compar. 4 Compar. 5 and Ex. I.

Two-ply friction material was also made at a 135 lb. basis weight. Thismaterial has Formulation #1 in the top layer, and a lower layer ofcotton and celite (Ex. I). This material was able to complete the testwith a 0.131 dynamic friction coefficient and 9 mils of wear. The lowerbasis weight friction material performed with lower dynamic frictioncoefficients.

The density of both 135 lb. and 200 lb. basis weight materials werecalculated using the equation below. High and low basis weight materialswere made into assemblies with a final density of 43.

D=BW*1/FLT*(1+PU)*0.004

where D=Density of Lining

BW=Basis Weight of raw material in lb./3000 sq.ft.

FLT=Final Lining Thickness in inches (after being saturated, cured, andcompressed)

PU=Resin Pick-up

(C) PAPER CAPILLARY FLOW

All the friction materials have mean pore size diameters that increaseafter the raw paper is resin saturated and cured, see Table 10 below.The two-ply materials have large larger mean pore size diameters thansingly-ply materials. This larger mean pore size diameter helps toincrease lubricant availability at the contact area.

Higher 200 lb. basis weight material, when raw or resin saturated andcured, has a relatively larger mean pore size diameter compared to thesame material at a lower 135 lb. basis weight. The raw 200 lb. basisweight Compar. 3 material has a 3.0016 micron mean pore diameter. Whenthe basis weight is reduced to 135 lb. material (Compar. 4), the meanpore size is reduced to 2.6170 microns. However, once compressed bothbasis weight materials have similar 2.45 micron mean pore sizediameters.

Two-ply materials with and without glass fibers in the lower layer (Ex.G and H, respectively) consistently have larger mean pore size diametersthan the single-ply materials. Altering the glass fiber concentration inthe lower layer composition does not have an influence on pore diameter.However, the various placement of two layers together with differentmean pore size diameters individually, is an effective method ofaltering the combined two-ply mean pore size.

Data for capillary flow shows mean pore size diameter increases (a) whenmaterial is saturated with resin and cured, and (b) when two-plymaterial is used compared to single-ply material. Mean pore sizedecreases when material is compressed after being saturated with resinand cured.

TABLE 10 Capillary Flow Analysis Five Measurements Per Friction MaterialMean Pore Size: A) raw paper, B) saturated (40%) and cured paper, C)saturated (40%), cured and compressed paper Raw Friction Pore SizeStandard Material Microns Deviation Compar. 3 A) 3.0016 0.2934 B) 4.08620.1044 C) 2.4433 0.0746 Ex. G A) 4.0160 0.3143 B) 4.6143 0.1758 C) Ex. HA) 3.5953 0.2565 B) 5.0581 0.2441 C) 2.8218 0.1717 Compar. 4 A) 2.61700.2781 B) 3.5227 (35% PU) 0.5261 C) 3.2854 (44% PU) 0.1513 D) 2.4645(44% PU) 0.1246 Ex. I A) 3.0512 0.1510 B) 3.7970 0.2665 C) 2.7396 0.3655

(D) LOWER LAYER WITH AND WITHOUT GLASS FIBERS

Compression Set Test

Compression set tests were performed to verify the presence of a “k”factor in the experimental materials. The “k” factor is a force constantdefined in the equation F(x)=−kx, wherein x is the distance a spring iscompressed or extending. D. Halliday and R. Resnick, “Fundamentals ofPhysics,” John Wiley and Sons, Inc., 1974. Using glass fibers in thelower layer composition alters the “k” factor of a two-ply material.

Tensile Tests on Raw Paper—Instron

Dry and wet tensile strength of a friction material is important duringhandling and resin saturating. Low tensile strength friction materialwill shred in the resin saturation bath. Table 11 below shows therelative strength of single-ply and two-ply material. A 30%-40% tensilestrength loss is measured when the friction material is wet withalcohol.

The 200 lb. basis weight Compar. 3 friction material is 50% higher inmachine and X-machine direction tensile strength than 135 lb. basisweight material. Two-ply 200 lb. basis weight material with cotton andcelite in the lower layer (Ex. G) has tensile strength similar to thesingle-ply production material.

When two-ply material has glass fibers included into the lower layer(Ex. H), tensile strength is reduced by 40%. This material has asubstantially lower tensile strength (66%) in X-machine directioncompared to the machine direction.

TABLE 11 Instron Tensile Test Data/Raw Paper Five Value Average - Dry &Wet Tests Tensile Strength (lbs.) Std. Dev. Raw Friction Material DryWet Dry Wet Compar. 3 Machine Direction 8.21 4.97 0.40 0.15 X-MachineDirection 5.48 3.43 0.20 0.16 Ex. G Machine Direction 7.84 4.90 0.880.50 X-Machine Direction 4.90 2.80 0.35 0.12 Ex. H Machine Direction5.15 2.90 0.65 0.37 X-Machine Direction 1.73 2.34 0.24 0.46 Compar. 4Machine Direction 4.16 2.72 0.36 0.13 X-Machine Direction 2.83 1.95 0.430.14

(E) PLY ADHESION OF THE RAW PAPER

Ply adhesion of a two-ply paper is defined as the resistance of layersto splitting when a force is applied at right angles to the faces of thesheet. This parameter is specifically useful for the ranking of rawfriction materials. Ply adhesion can be increased through saturating asheet with almost any polymeric material. Three factors can effect theply adhesion of latex saturated papers: (1) the quantity and kind ofpolymer in the sheet, (2) the adhesion of the polymer to the fibers, and(3) the arrangement of the fibers in the sheet. The latex can provideadditional ply adhesion to the two-ply material until the phenolic resinhas been cured.

The above Example II shows that single-ply and two-ply materialsresulted in similar Full Pack frictional performance. However, lowerbasis weight friction materials result in lower dynamic frictioncoefficients.

When basis weight of a friction material is lowered the liningdurability is reduced. Two-ply material is more durable than single-plymaterial when tested at the lower basis weight.

The mean pore size diameter is altered when friction materialcomposition is changed. Changing composition of the primary layer in atwo-ply material increases pore size and improves clutch assemblylubrication.

The cost savings result from using two-ply material as compared tosingle-ply material. More exotic and expensive materials can be used inthe secondary layer which, in preferred embodiments, can be relativelythin. Ingredients that significantly improve clutch friction and/or wearperformance can be concentrated in the secondary layer.

EXAMPLE III

Materials with a high energy capacity are required in some clutchapplications. Typically, high friction coefficient is not as importantas a high thermal resistance from such material. The energy capacity ofthe friction materials can be increased by utilizing an elastomericparticle in the formulations. Further, the use of the two-ply frictionmaterial with silicone as a saturated resin increases the frictioncoefficient and reduces wear. The comparative examples and Ex. Iformulations are shown in Table 12 below.

TABLE 12 Compar. 6 One-Ply of Formulation #2: cotton 46%, celite 17%,aramid fiber 6%, silicon nitride particles 6%; Friction particles:nitrile rubber type elastomeric polymer 5%, CNSL-5%, very hard CNSL-15%,Latex 2% processing aid Total Basis Wt. 133-135, Caliper = 0.025″Compar. 6a Saturated with 43% Phenolic Compar. 6b Saturated with 35%Phenolic Compar. 7 One-Ply Formulation #1A: Same as Formulation 1,except including nitrile type elastomeric friction particles, ratherthan isoprene type particles Total Basis Wt. ^(˜)135, Caliper = 0.021-0.022″ Compar. 7a Saturated with 45% Phenolic Compar. 7b Saturated With34% Phenolic Compar. 7c Saturated with 47% Silicone Ex. I First-Plycotton 60% celite 40% Second-Ply of Formulation #1 Total Basis Wt.130-140, Caliper = 0.022-0.0235″ Ex. Ia Saturated with 56% Silicone Ex.Ib Saturated with 43% Silicone Compar. 3 One-Ply of Formulation #1 TotalBasis Wt. 135, Caliper 0.021- 0.023″

Compar. 7 formulations were saturated with phenolic resin (Compar. 7a,7b) and a silicone resin (Compar. 7c) separately. Compar. 3 and Ex. Iaand Ib were saturated with a silicone resin.

High energy friction material Compar. 6 that contains three differenttypes of friction particles was made. This material was saturated withphenolic resin.

All materials were 135 lb. basis weight and used for making clutchassemblies. The assemblies were evaluated for friction and wearcharacteristics according to procedures 528C or 527C.

Full Pack Test—Moderate Energy Procedures 528C

(A) Phenolic Resin

When the one-ply material is made with the nitrile friction particlereplacing the isoprene friction particle (as in Compar. 7), thedurability is slightly increased. The Compar. 3 material (with theisoprene particle) at 35% pick-up lasted 600 cycles, while the Compar. 7material at the same pick-up lasted 850 cycles. A summary of thefriction and wear data is given in Table 13 below. Surface appearancedata and percent dynamic friction data can be found in Table 14 below.

TABLE 13 Full Pack Test - Laboratory Data at Cycle 1050 Procedure 528C -135 lb. Basis Weight Material Exxon 1975 Type “H” Lubrication Low SpeedHigh Speed Pack Loss Friction Material Dyn.* Dyn.** Mils Compar. 6a0.138 0.146  7.0 Compar. 6b NA 0.132 36.0 Compar. 7a 0.125 0.123  4.0Compar. 7b NA 0.133 @ 12.0 @ cycle 850 cycle 850 Compar. 7c 0.142 0.151 0.0 Ex. Ia 0.162 0.175  5.0 Ex. Ib 0.159 0.172  6.0 Compar. 3- 0.1470.155  0.0 Silicone 45% Compar. 3- NA 0.133 @ stopped Phenolic 40% cycle550 Compar. 3- NA 0.135 @ stopped Phenolic 35% cycle 600 Ex. I- NA 0.131 9.0 Phenolic 41% * Low speed dynamic (static) recorded according to the45 degree method described in drawing #95407 ** High speed dynamicrecorded 0.2 seconds after engagement

TABLE 14 Full Pack Test - Pack Surface Appearance Data Procedure 528C -135 lb. Basis Weight Material Exxon 1975 Type “H” Lubrication FrictionDelam- Material Abrasion Breakout Glazing ination % Fade** Compar. 6b 20 2 0 0.0 Compar. 6a 5 0 3 0 13.7 Compar. 7a 2 1 2 0 8.1 Compar. 7b 4 @cycle 0 @ cycle 4 @ cycle 0 @ cycle NA 850 850 850 850 Compar. 7c 0 0 10 16.1 Ex. Ia 0 0 1 0 8.4 Ex. Ib 0 0 1 0 8.0 Comp. 3 0 0 1 0 10.4Compar. 3 4 @ cycle 0 @ cycle 2 @ cycle 0 @ cycle NA Phenolic 650 650650 650 44% Compar. 3 5 @ cycle 0 @ cycle 3 Ε cycle 0 @ cycle NAPhenolic 650 650 650 650 35% Ex. I 1 0 3 0 5.8 Phenolic 41% ** Percenthigh speed dynamic friction face from cycle 200 to 1050

Assemblies made with Compar. 7 material at a higher 45% pick-up level,were able to successfully complete the 528C type test. This material,which includes the nitrile type elastomeric friction particle, had afinal dynamic friction of 0.123 and only 4.0 mils pack loss. The Compar.7 material tested with a 8.1% dynamic friction fade. Abrasion andglazing were ranked “2”, while breakout was “1”, and delamination a “0”.In comparison, the one-ply material (Compar. 3) with a 44% phenolicresin pick-up was stopped after 550 cycles. There is essentially noimprovement when resin pick-up goes from 35% to 44% with one-plymaterial. Exchanging the isoprene elastomeric friction particle with thenitrile elastomeric friction particle in the formulation #1A, andincreasing resin pick-up, gives the material additional energy capacity.

The Compar. 7 material was saturated with silicone resin at a 47%pick-up level. This material had a final dynamic friction coefficient of0.151, with 16.1% dynamic friction fade. The pack loss was 0.0 mils.Surface appearance was excellent after testing. The abrasion, breakout,and delamination were all ranked “0”, while the glazing was “1”. Usingsilicone resin in conjunction with nitrile elastomeric friction particlein the formulation #1A increases lining wear resistance, frictioncoefficient, and improves assembly surface appearance rankings.

Single-ply material (Compar. 3) at 135 lb. basis weight was unable tosuccessfully complete the 528C test with 40% or 35% phenolic resinpick-up, as seen Table 13 above. These tests were stopped after roughly600 cycles.

However, the two-ply material with formulation #1 as the top layer (Ex.I), and 41% phenolic resin pickup, was able to successfully complete thetest with a final dynamic friction coefficient of 0.131, 5.8% frictionfade, and 9.0 mils of pack loss, as seen Table 13 above.

When the single-ply material (Compar. 3) is saturated with siliconeresin at 45% pick-up, the final dynamic friction increases to 0.155 witha 10.4% friction fade, and 0 mils pack loss, as seen Table 13 above.Assembly surface glazing was ranked “1” and abrasion, breakout, anddelamination all ranked “0”. The use of the silicone resin has improvedthe friction and wear performance of one-ply friction material underthese test conditions.

The two-ply material (Ex. I) which has Formulation #1 on the top wassaturated with a silicone resin at 43% and 56% pick-up levels. Bothtests had a final dynamic friction level of roughly 0.174 with about 5.5mils of pack loss and 8.2% friction fade. Surface condition of thelining was excellent after testing. Only glazing was ranked “1”,abrasion, breakout, and delamination were all ranked “0.” The two-plymaterial resulted in high friction than the single-ply material. Again,the Formulation #1 material with the silicone performed with higherfriction than the phenolic resin saturated material.

FIG. 5 shows the number of cycles versus friction curves for formulationmaterial with the alterations made for increasing durability andfriction for the Compar. 3 and Ex. I. The differences in the curves showthe effect of the elastomeric 4198 particle, the silicone resin, and thetwo-ply material.

EXAMPLE IV

A variation in friction material density influences the friction andwear performance of an assembly. The single-ply material and two-plymaterials with different density combinations have been evaluated.Two-ply material density combinations evaluated were primary andsecondary layers having the same density (Ex. J), primary layer having ahigh density and secondary layer having a low density (Ex. K), andprimary layer having a low density and secondary layer having a highdensity (Ex. L), as seen in Table 15 below.

The same material formulation was used for both the primary (bottom) andsecondary (top) layers of the two-ply friction material. However, theexamples which comprise high density layers contain more “mechanically”refined cotton material. The refining of the cotton fibers increases thefibrillation of the fibers and lowers the Canadian Standard FreenessNumber (CFN). The CFN (as tested by the T227om-94 Test Method approvedby the TAPPI) becomes low as the amount of refining or fibrillation ofthe fiber material increases. The density increases as the amount offibrillation increases (i.e., as the CFN decreases). It is to beunderstood that “normal” or standard cotton fibers have an average CFNof about 550, while extra “refined” cotton fibers have an average CFN ofabout 450. Thus, the standard cotton fibers (about 550 CFN) producerelatively low density sheets or layers of fibrous base material whilethe refined cotton fibers (about 450 CFN) produce relatively highdensity sheets or layers of fibrous base material.

In all cases, the total paper basis weight was targeted to about 200lbs., of which the primary and secondary layers were 160 lbs. and 40lbs., respectively. A phenolic saturating resin was used to obtain a50-55% pick-up. All the tests were run according to procedure 498 withExxon 1975 Type “H” lubrication.

The friction materials below contain Formulation #3: cotton 36.8%,aramid pulp 4.8%, celite 13.6%, silicon nitride particles 4.8%, frictionparticles: nitrile, elastomeric polymer particles: 4.0%, CNSL 4.0%, veryhard CNSL 12.0%; novoloid fibers: 3 mm length 10%, 0.20 mm length 10%.

The porosity data listed in Table 15 below was a measure of the lengthof time required to pass a specific volume of air through a sheet ofpaper using a Gurley Densometer.

The Mullen's data presented in Table 15 below is a test method whichmeasures the bursting strength of paper when pressure is applied at aconstant rate to a liquid controlled by a rubber diaphragm under astandard orifice covered by a test specimen. This test method is anextrapolation of TAPPI Method T-403.

TABLE 15 Satu- Raw rated Dry Wet Den- Den- Tensile Tensile PorosityMullen sity sity Ex. J - Total 6000 5000 3 12 20.88 42.9 (primary andsecondary layer) Basis Wt. = 201, Caliper = 0.0385″ Primary Layer: 55004000 2 9 19.63 Basis Wt. = 159.5 Caliper = 0.0325″ Ex. K - Total 58004700 3 12 24.5 48.5 (primary and secondary layer) Basis Wt. = 196,Caliper = 0.032″ Primary Layer: 5000 4000 2 9 21.83 Basis Wt. = 155.5,Caliper = 0.0285″ Ex. L - Total 6900 5800 4 14 21.1 42.9 (primary andsecondary layer) Basis Wt. = 204, Caliper = 0.0385″ Primary Layer: 58004500 3 11 20.5 Basis Wt. = 164, Caliper = 0.032″

The two-ply material, with the same density and material formulation inboth layers, results with similar dynamic friction magnitude at both2000 rpm (from 0 to 100 cycles) and 4800 rpm (from 101-2100 cycles)engagement speeds (Ex. J). FIG. 6 illustrates the friction versus numberof cycle curves from tests with two-ply assemblies for Ex. J. The totalpack loss was 2.8 mils.

FIGS. 7 and 8 show two-ply material having density variations. FIG. 7shows the static and dynamic coefficients of friction for Ex. K. Thetotal pack loss was 0.2 mils.

FIG. 8 shows the static and dynamic coefficients of friction for Ex. L.The total pack loss was 2.2 mils. Altering the density of either theprimary or secondary layer of two-ply material changes the friction andwear performance. The most favorable performance, as shown by theporosity data, resulted with the primary and secondary layers of low andhigh density, respectively (Ex. L) as shown in FIG. 8.

Ex. L shows improved static and dynamic friction coefficients during the2000 rpm engagements and slightly higher friction coefficients. Assemblywear resistance is also very good with this material. FIGS. 6-8illustrate the friction versus number of cycle curves the three two-plymaterial density combinations evaluated (Ex. J, K and L).

Two-ply materials perform better than single-ply materials. The besttwo-ply material has a low density primary layer and a high densitysecondary layer combination. The two-ply materials exhibited slightlymore wear resistance than single-ply material. The dynamic frictioncoefficients from tests with two-ply materials were less fluctuating atdifferent engagement speeds compared to those from the single-plymaterial.

EXAMPLE V

The friction and wear tests were performed according to Procedure 5004Awith Exxon 1975 Type “H” ATF. All results were obtained using theone-ply friction material or a two-ply friction material. Selectedmodified and unmodified silicone resins were evaluated with these twofriction materials. The materials tested are shown in Table 16 below.Both Ex. M and N contain Formulation #4 as follows: aramid pulp—32%,celite—26%, silica—16%, friction particles: nitrile type elastomericparticles—16%, glass fibers 10%.

TABLE 16 Ex. M Single-ply of Formulation #4 Basis Wt. 115-125 Ex. NTwo-ply of Formulation #4 Basis Wt. 115-125 Primary Layer Basis Wt. 80 -low density Secondary Layer Basis Wt. 40 - high density

Samples saturated with the modified silicone resins have almost twicethe shear strength compared to samples saturated with an unmodifiedsilicone resin. Samples saturated with the modified silicone resinsincrease if mixed with a phenolic or other “brittle” type resin.

Even though the modified silicone resins have higher shear strength thanthe unmodified resins, they result in similar or slightly higher setvalues than the unmodified silicone resins. There appears to be littlecorrelation between high shear strength and high unmodified siliconecompression set resistance with these friction material formulations.Mean pore size diameter tends to be slightly larger in samples saturatedwith low cross-linked resins compared to the high cross-linked resins.

Impressive friction and wear performance was exhibited with a two-plymaterial which had been saturated with a silicone resin subjected to a450° F. cure. This material had only 0.8 mils pack loss and 9% fictionfade. However, the same material cured at 400° F. tested with 21.0 milsof pack wear and 13% friction fade. Thus, when silicone resin was usedthere was better pack loss performance and friction performance, whichreflects the proper curing of the resin.

A two-ply fibrous base material was saturated with the differentsilicone resins listed below. The material has its first TGA peak atapproximately 592° C., and a 55.46 weight percent residue as seen inFIG. 9. All were materials saturated to a 60%-65% weight pickup with theresins as shown in Table 17 below.

TABLE 17 Resin 1) MTV Silicone Rubber, Resin/Polymer Ratio = 50:50 - 30min. @ 400° F. - silicone Resin 2) 30 min. @ 450° F. - modified siliconeWt. Avg. Mol. Wt. = 10,000, Degree of Crosslinking = 1.3 Resin 3) 30min. @ 450° F. - modified silicone Wt. Avg. Mol. Wt. = 10,000, Degree ofCrosslinking = 1.4 Resin 4) 30 min. @ 450° F. - 20:80 -silicone/phenolic blend Resin 5) MTV Silicone Rubber, Resin/PolymerRatio = 50:50 - 30 min. @ 450° F. - silicone Resin 6) 30 min. @ 450°F. - modified silicone Wt. Avg. Mol. Wt. = 10,000, Degree ofCrosslinking = 1.4 Resin 7) 30 min. @ 400° F. - modified silicone Wt.Avg. Mol. Wt. = 5000,000, Degree of Crosslinking = 1.4 Resin 8) 30 min.@ 450° F. - modified silicone Wt. Avg. Mol. Wt. = 5000,000, Degree ofCrosslinking = 1.4 Resin 9) Silicone Rubber, Resin/Polymer Ratio = 70:30Resin 10) Silicone Rubber, Resin/Polymer Ratio = 90:10 Resin 11)Silicone Rubber, Resin/Polymer Ratio = 5:95

The physical test data for the high temperature friction materialsExample M—a single-ply of formulation #4 and Example N—a two-ply offormulation 4 which were saturated with variations of silicone and asilicone/phenolic blend are shown in Table 18 below.

TABLE 18 MATERIAL PHYSICAL ATTRIBUTES Silicone Resin ComparisonCompression Tensile - Relaxation Mean Pore Saturating Shear - lb/in @1500 Diameter - Resin lb/in² (not il/in²) lb/in² microns Single-PlyMaterial Ex. M Resin 1 183, 208, 201 20, 22, 21 Comp. = 0.4581″, 3.3378Set = 0.1067″ 3.1466 Resin 9 226, 236, 234 27, 26, 27 Comp. = 0.4240″,3.0059 Set = 0.1142″ 2.9611 Resin 11 84, 90, 85 11, 10, 10 Comp. =0.4792″, 3.5825 Set = 0.1718″ 3.1183 Two-Ply Material Ex. N Resin 1 172,162, 146 23, 22, 23 Comp. = 0.3666″, 2.8875 Set = 0.0630″ 3.3010 Resin 2417, 373, 358 45, 45, 44 Comp.= 0.3449″, 3.7316 Set = 0.1081″ 3.5069Resin 3 355, 355, 330 43, 42, 43 Comp. = 0.3432″, 2.7773 Set = 0.1460″2.7956 Resin 4 406, 442, 412 52, 44, 55 Comp. = 0.2251″, 2.8180 Set =0.0524″ 2.3375 Resin 5 188, 226, 213 28, 29, 29 Comp. = 0.4181″, 3.2174Set = 0.1056″ 2.7459 Resin 6 374, 332, 357 41, 45, 43 Comp. = 0.3490″2.6725 Set = 0.1436″ 2.5462 Resin 7 379, 401, 388 43, 44, 42 Comp. =0.3642″, 2.5392 Set = 0.1864″ 2.8858 Resin 8 336, 344, 359 41, 43, 42Comp. = 0.3878″, 2.9224 Set = 0.1919″ 2.7483

Friction and wear data was performed according to SAE procedure 5004Ausing Exxon 19875 Type “H” ATF lubrication. A summary of the results areprovided in the Table 19 below.

TABLE 19 Test Procedure 5004A - Exxon 1975 Type “H” ATF Silicone ResinComparison A-Cycle 50 B-Cycle 2050 C-Cycle 2100 Wear Saturating Resin uiuf ui uf ui uf inches Single−Ply Material Ex. M Resin 1 Ex. M-1 0.1680.165 0.133 0.145 0.139 0.159 −0.0024 Fade* 0.0% +3.8% −17.4% −7.1%+3.7% −0.6% (T136) Resin 9 Ex. M-2 0.177 0.169 0.145 0.139 0.161 0.1550.0012 Fade −2.2% +7.0% −20.8% −15.2% −4.6% −1.3% (T230) Resin 11 Ex.M-3 0.159 0.153 0.095@550 0.147@550 NA NA 0.0276 Fade −2.5% +2.0% −33.1%−14.5% (T231) Two-Ply Material Ex. N Resin 1 0.187 0.174 0.168 0.1520.178 0.161 0.0210 Fade −2.1% +6.1% −12.0% −13.1% +3.5% 0.0% (T225)Resin 2 0.166 0.155 0.144@1650 0.127@1650 NA NA 0.0029 Fade +5.7% +6.2%−3.4% −9.9% (T183) Resin 3 0.164 0.155 0.136@1950 0.129@1950 NA NA0.0132 Fade +3.8% +6.9% −16.6% −10.4% (T222) Resin 4 0.118 0.129 0.1100.122 0.130 0.136 0.0059 Fade −2.5% +2.4% −16.7% −4.7% +2.4% +0.7%(T223) Resin 5 0.171 0.151 0.155 0.145 0.150 0.155 0.0008 Fade −2.3%0.0% −9.4% −7.1% +4.2% +2.0% (T216) Resin 6 0.163 0.158 0.135@15500.128@1550 NA NA 0.0149 Fade +5.2% +12.9% −19.6% −13.5% (T224) Resin 70.164 0.155 0.108@750 0.126@750 NA NA 0.0189 Fade −7.9% +4.0% −28.0%−16.0% (T185) Resin 8 0.171 0.161 0.122@850 0.127@850 NA NA −0.0057 Fade−1.2% +3.9% −26.5% −21.1% (T226)

The two-ply material tests were evaluated using different resins, thesilicone and silicone/phenolic resin. The silicone material that wascured to 450° F. rather than 400° F. resulted in 0.8 mils pack losscompared to 21.0 mils pack loss with the same material cured to 400° F.The two-ply material saturated with a silicone/phenolic resin mixtureresulted in 5.9 mils wear.

Two TMA (Thermal Mechanical Analysis) tests were performed: the firsttest involved the heating of the materials at 10° C./minute incrementsto 750° F. (Method “A”) while measuring dimensional displacement, thesecond test involved five thermal cycles from ambient to 500° C. andthen a final temperature increase to 750° C. (Method “B”).

TABLE 20 MATERIAL THERMAL COMPARISON Silicone Resin ComparisonTMA-Method “A” TMA-Method “B” Saturating 30 C.-750 C. 30 C.-500 C., then750 C. Resin 1st-Peak 2nd-Peak 1st-Peak 2-Peak Single-Ply Material Ex. MResin 1 +44.57u −23.72u  +43.05u −14.6u  @ 273.4 C. @ 507.4 C. @ 274.5C. @ 513.82   Resin 9 +26.81u −15.99u −40.3U  @ 270.0 C. @ 520.1 C. @742.6 C. Resin 11 +40.83u −10.37u +53.5u +583.9u @ 294.9 C. @ 443.1 C. @326.2 C. @ 592.3 C. Two-Ply Material Ex. N Resin 1 +48.80u −23.15u+40.1u +474.1u @ 280.7 C. @ 505.9 C. @ 287.9 C. @ 734.3 C. Resin 2+30.30u +23.8u  +40.3u +265.6u @ 271.4 C. @ 551.8 C. @ 287.7 C. @ 552.0C. Resin 3 +23.78u +12.8u +13.8u  @ 270.1 C. @ 266.2 C. @ 555.5 C. Resin4 +22.62u −44.22u +540.2u @ 282.2 C. @ 491.1 C. @ 576.7 C. Resin 5+44.69u −12.24u +29.2u −24.9u  @ 287.9 C. @ 487.9 C. @ 291.2 C. @ 503.7C. Resin 6 +23.61u +19.9u −18.6u  @ 275.4 C. @ 271.7 C. @ 598.5 C. Resin7 +2.73u  −20.89u −63.5u +248.0u @ 257.6 C. @ 427.2 C. @ 619.0 C. @740.5 C. Resin 8 −7.86u  −43.47u +14.9u +458.4u @ 257.6 C. @ 491.6 C. @287.2 C. @ 739.0 C. *Level A: ui = friction at 3600 rpm, um = 1850 rpm,uf = 740 rpm, and us = 0.72 rpm. Level B: ui = friction at 3600 rpm, um= 1850 rpm, uf = 740 rpm, and us = 0.72 rpm. Level C: ui = friction at3600 rpm, um = 1800 rpm, uf = 740 rpm, and us = 0.72 rpm.

FIG. 9 shows a Thermalgavimetric analysis (TGA) of the Example N. TheTGA curve shows a higher temperatures which indicates increase heatresistance. The percent change in weight was 35.15%. The less rapid theweight loss, the more heat resistance the friction material possesses.

EXAMPLE VI

A high performance two-ply paper composite wet clutch facing frictionmaterial comprises a secondary layer which comprises a high temperature,high energy, low compression set material formulation, and a primarylayer which comprises a non-linear elastic, porous formulation. Thetwo-ply composite material is highly porous, non-linearly elastic andhas a low compression set. Friction materials, including for example,two-ply composite wet clutch facings show substantial improvement infriction performance over a single-ply material of the secondary layermaterial when used alone.

The secondary layer comprises Formulation #5 which contains about 10% toabout 40% porous activated carbon particles, about 10% to about 30%cotton fibers, about 5% to about 30% precision cut aramid fibers, about0-20% synthetic graphite and about 0-40% fillers. The primary layercomprises Formulation #6 which contains about 5% to about 30% non-linearelastic PET fibers, about 20% to about 60% cotton fibers, about 10% toabout 40% fillers. In a preferred embodiment, the primary layercomprises about 55% cotton, about 10% non-linear elastic PET fibers; 35%celite, and about 2% latex, processing aids, and the secondary layercomprises about 30% activated carbon particles, about 25% cotton, about10% aramid fiber, about 10% aramid pulp, about 25% celite, and about 2%latex processing aids. The secondary layer comprises about 5% to about30% and most preferably about 20% of the total thickness of the two-plycomposite material. The resulting two-ply composite material is highlyporous and non-linearly elastic. The two-ply composite material whenused in wet clutch facings shows substantial improvement in frictionperformance over a single-ply layer high temperature material.

TABLE 21 Compar. 8 Formulation #5 45% phenolic resin PU Final density47.4 lb/cu ft. Compar. 9 Formulation #6 Ex. 0 Secondary layer ofFormulation #5 Primary layer of Formulation #6 44% phenolic resin PUFinal density 44.4 lb/cu ft

The samples where saturated with a phenolic resin at the noted pick-uplevels. The data shown in Table 22 shows the average pore diameter inmicrons for the Compar. 8, Compar. 9 and Example O. It is seen that theExample O two-ply material has an average pore diameter which is greaterthan either the Compar. 8 or 9. All samples are cured and compressed toa final density of 45-47 lb/cu. ft.

TABLE 22 Aver. Pore Diameter (microns) Compar. 8 2.599 Compar. 9 3.845Ex. 0 3.894

The compression-relaxation tests were conducted using the Compar. 8,Compar. 9 and Ex. O. Compressibility is the measure of a materials'ability to return to its original size after being compressed.

The high speed dynamic coefficient of friction versus cycle data, forthe Compar. 8 and Ex. O using a full, pack test (527C) high energy testare shown in FIG. 13.

The two-ply friction material is highly porous and non-linear elastic.There is a substantial improvement in friction performance over thesingle ply of the Compar. 8 or 9. There is a 10 to 25% increase indynamic coefficient of friction and about a 20 to 50% increase in wearresistance.

In addition there is an increase in heat resistance and there is a lowerstatic/dynamic ratio. The two-ply friction material has an increasedpore size, a low compression-relaxation behavior, and an overallincrease in resin pickup over the one-ply materials.

FIG. 10 shows the compression and compression set for the Compar. 8.FIG. 11 shows the compression and compression set data for Compar. 9.FIG. 12 shows the compression and compression set for Ex. O.

EXAMPLE VII

A high performance two-ply friction material comprises a secondary ortop layer which comprises a less porous, high temperature resistance,high thermally conductive, high energy and high strength materialformulation, and a primary layer which comprises a more porous, highthermally convective material formulation. The two-ply frictionmaterials show substantial improvement in friction performance oversingle-ply materials.

The secondary layer comprises Formulation #7 which comprises about 0 toabout 30% cotton fibers; about 5 to about 45% more fibrillated aramidfibers having about 525 CSF or less; about 5 to about 35% fillers; about0 to about 30% carbon particles and/or graphite; about 5 to about 30%carbon fibers; about 1 to about 10% novoloid fibers; and about 0 toabout 3% latex processing aids.

The primary layer comprises Formulation #8 which comprises about 20 toabout 60% cotton fibers; about 10 to about 30% less fibrillated aramidfibers having about 525 CSF or greater; about 10 to about 30% fillers;about 10 to about 30% graphite and/or carbon particles; and about 0 toabout 3% latex processing aids.

Example P comprises a secondary layer having about 43% less fibrillatedaramid fibers, about 30% filler, about 15% carbon particles, about 10%carbon fibers, about 2% novoloid fibers, and about 2% latex processingaids; and a primary layer having about 40% cotton fibers, about 20% morefibrillated aramid fibers, about 20% fillers, about 20% graphite, andabout 2% latex processing aids.

Table 23 below shows the raw paper properties of the Examples P-1 andP-2. The dry and wet tensile strengths of a friction material areimportant during handling of the material and resin saturating of thematerial. Low tensile strength friction materials will shred in theresin saturation bath. The two-ply materials have good wet and drytensile strengths.

TABLE 23 Raw Paper Properties P-1 P-2 Basis Weight lb/3000 ft2 168 171.8Caliper inch 30.5 30 Dry Tensile 6106 5307 Wet Tensile 4081 3989 550° C.Ash 36.2 36.27 900° C. Ash 17.7 19.51 Densometer 6.4 6.8 Basis Weightlb/3000 ft2 168 170 Caliper inch 31 29.5 Dry Tensile 5995 5120 WetTensile 4051 3990 550° C. Ash 34.98 36.1 900° C. Ash 17.35 19.3Densometer 6.8 6

In order to obtain information about the porosity, or relative lubricantpenetration characteristics, of the primary layer and the secondarylayer, oil drop times were evaluated. These times generally reflect oilabsorption characteristics of a material. Table 24 below shows that theprimary or bottom layer is more porous than the secondary or top layer,both for the raw paper and for a friction material impregnated withabout 50% resin pick-up. The Table 24 shows that the higher rate (lesstime) for oil penetration, the more porous the material.

TABLE 24 Oil Drop Results Raw Paper 50% Resin Pick-Up Top Layer LowerLayer Top Layer Lower Layer P-1 3.14 2.53 6.6 6.22 P-2 3.4 2.51 7.875.31

Table 25 below shows the high speed, high energy test results of ExampleP, with 49.2% resin pick-up as compared to a conventional single-plyfriction material. The Example P has more cycles before failure (5800 v.1339 cycles). Also the Example P has better stop times and thecoefficient of friction stability is much higher for Example P than forthe single-ply material.

TABLE 25 Conventional Layer Ex. P-2 Basis Wt. lb/3000 ft² 172 Thicknessmils 0.030  Density lbs/inch³ 0.0133 Final thickness 0.021″ 0.021″ PU %40% 49.2% Level A (3700 rpm, 0.157 lb.ft.sec2) Coefficient μi μd μO μiμd μO  1 cycle 0.135 0.122 0.125 0.115 0.111 0.117 10 cycle 0.152 0.1420.142 0.124 0.118 0.126 20 cycle 0.149 0.144 0.143 0.126 0.120 0.128 30cycle 0.154 0.143 0.140 0.128 0.122 0.131 50 cycle 0.152 0.142 0.1380.132 0.124 0.130 μd change % 16.4 11.7 Level B (3700 rpm, 0.14lb.ft.sec2) Coefficient μi μd μO μi μd μO 185 cycle 0.129 0.124 0.1070.116 0.115 0.107 198 cycle 0.128 0.125 0.107 0.117 0.115 0.107 211cycle 0.129 0.125 0.107 0.115 0.114 0.109 224 cycle 0.127 0.125 0.1070.115 0.114 0.108 Average μ Stoptime Lebel B 0.808 0.802  250 cycle0.125 0.125 0.108 0.117 0.115 0.108  450 cycle 0.120 0.122 0.105 0.1160.114 0.109  750 cycle 0.110 0.117 0.104 0.118 0.113 0.105 1150 cycle0.107 0.110 0.105 0.113 0.111 0.102 1650 cycle 0.118 0.112 0.102 2650cycle 0.115 0.116 0.100 3650 cycle 0.115 0.109 0.097 4650 cycle 0.1160.110 0.096 5650 cycle 0.104 0.112 0.101 7650 cycle 8650 cycle End ofTest Cycles 1339 cycles 5800 cycles μ around end of Test 0.113 (1330cycles) 0.113 (5790 cycles) Stoptime at end 0.881 0.859 Change of 0.68mm 0.82 mm Displacement Total wear (in) 0.0154″ 0.0205″ Failure ModeSTTM > 10% up thickness change failure Friction plates Abrasion Glazing,Cracking Erosion Surface flacking Radial path destruct Scoring Separatorplates Heat stains Heavy heat stains Some warpage Hot spots Slope ofstoptime Very steep Mid, and goes down Slope of thickness Flat, but jumpup Flat, but slight jump change

The shear strength data contained in Table 26 below shows that shearfailure is not at the two-ply interface. The interface strength betweenthe top layer and the bottom layer is sufficient so that there is nodelamination which occurs during use of the two-ply friction material ofthe present invention.

TABLE 26 Shear Results: 40% PU Upper Layer Fracture Furnish HighlightShear, PSI Ex. P-1 Upper 43%K 1030/20%CF- 333 247/20%C-281 Ex. P-2 Lower43%K 1030/10%CF- 369 247/30%C-281

INDUSTRIAL APPLICABILITY

The present invention is useful as an energy friction material for usewith clutch plates, transmission bands, brake shoes, synchronizer rings,friction disks or system plates and torque converters.

The above descriptions of the preferred and alternative embodiments areintended to be illustrative and are not intended to be limited upon thescope and content of the following claims.

What is claimed is:
 1. A two-ply fibrous base material for use in anon-asbestos friction material comprising a secondary or top layerbonded to a primary or lower layer, the primary layer comprisingnon-linearly elastic fibers, cotton fibers, and filler material; thesecondary layer comprising carbon fibers, aramid fibers, fillermaterial, and novoloid fibers, wherein the primary layer has a porositywhich is higher than the secondary layer.
 2. The two-ply fibrous basematerial of claim 1, wherein the secondary layer comprising from about2% to about 50% of the total combined two-ply thickness.
 3. The two-plyfibrous base material of claim 1, wherein the primary layer comprises,in percent, by weight, based on the weight of the primary layer: about 5to about 30% non-linearly elastic fibers, about 20 to about 60% cottonfibers, about 10 to 40% filler material, and about 0 to about 30%graphite, about 0 to about 30% carbon particles, and about 0 to about 3%latex type processing aids.
 4. The two-ply fibrous base material ofclaim 1, wherein the primary layer comprises about 20% less fibrillatedaramid fibers; about 40% cotton; about 20% filler material; and about20% graphite, carbon particles or a mixture of graphite and carbonparticles, based on the weight of the primary layer.
 5. The two-plyfibrous base material of claim 4, wherein the primary layer has about20% graphite.
 6. The two-ply fibrous base material of claim 1, whereinthe non-linearly elastic fibers of the primary layer comprise lessfibrillated aramid fibers having a Canadian Standard Freeness of about525 or greater and the aramid fibers of the secondary layer comprisemore fibrillated aramid fibers having a Canadian Standard Freeness ofabout 525 or less.
 7. The two-ply fibrous base material of claim 1,wherein the secondary layer comprises, in percent by weight based on theweight of the secondary layer, about 10% carbon fibers, about 43% aramidfibers, about 30% filler material; about 15% carbon particles, graphiteor a mixture of carbon particles and graphite; and, about 2% novoloidfibers.
 8. The two-ply fibrous base material of claim 7, wherein thesecondary layer has about 15% carbon particles.
 9. The two-ply fibrousbase material of claim 1, wherein the novoloid fibers comprise about 1to about 10% fibers having an average length of about 3 mm and about 5to about 15% fibers having an average length of about 0.2 mm.
 10. Thetwo-ply fibrous base material of claim 1, wherein the secondary layercomprises about 2% cotton fibers.
 11. A non-asbestos friction materialcomprising a two-ply fibrous base material of claim 1 impregnated with aphenolic or modified phenolic resin, a silicone or modified siliconeresin, or a blend of a phenolic or modified phenolic resin with asilicone or modified silicone resins.
 12. The friction material of claim11 wherein the modified phenolic resin comprises an epoxy phenolicmodified resin.
 13. The friction material of claim 11, wherein thefriction material comprises about 30% to about 65% resin, by weight. 14.A friction material according to claim 11, comprising a clutch facing.15. A friction element according to claim 11, comprising a brake shoelining.
 16. A process for producing a two-ply fibrous base materialcomprising forming a primary layer comprising non-linearly elasticfibers, cotton fibers and filler material; and adhering a secondarylayer to the primary layer, the secondary layer comprising carbonfibers, aramid fibers, filler material, and novoloid fibers; wherein theprimary layer has a porosity which is higher than the secondary layer.17. A process for producing a non-asbestos friction material comprisingimpregnating the two-ply fibrous base material of claim 16 with aphenolic or modified phenolic resin, a silicone or modified siliconeresin, or a blend of a phenolic or modified phenolic resin with asilicone or modified silicone resin and thereafter heating theimpregnated two-ply fibrous base material to cure the resins.
 18. Atwo-ply fibrous base material for use in a non-asbestos frictionmaterial comprising a secondary or top layer bonded to a primary orlower layer, the primary layer comprising non-linearly elastic fibers,cotton fibers, and filler material; and wherein the secondary layercomprises, in percent by weight based on the weight of the secondarylayer: about 5 to about 30% carbon fibers, about 0 to 30% cotton fibers,about 5 to about 45% aramid fibers, about 0 to about 30% graphite, about0 to about 30% carbon particles, about 5 to about 35% filler material,about 1 to about 10% novoloid fibers, and about 0 to about 3% latex typeprocessing aids.
 19. The two-ply fibrous base material of claim 18,wherein the secondary layer comprises from about 2% to about 50% of thetotal combined two-ply thickness.
 20. The two-ply fibrous base materialof claim 18, wherein the primary layer comprises, in percent, by weight,based on the weight of the primary layer: about 5 to about 30%non-linearly elastic fibers, about 20 to about 60% cotton fibers, about10 to 40% filler material, and about 0 to about 30% graphite, about 0 toabout 30% carbon particles, and about 0 to about 3% latex typeprocessing aids.
 21. The two-ply fibrous base material of claim 18,wherein the primary layer has a porosity which is higher than thesecondary layer.
 22. The two-ply fibrous base material of claim 18,wherein the primary layer comprises about 20% less fibrillated aramidfibers; about 40% cotton; about 20% filler material; and about 20%graphite, carbon particles or a mixture of graphite and carbonparticles, based on the weight of the primary layer.
 23. The two-plyfibrous base material of claim 22, wherein the primary layer has about20% graphite.
 24. The two-ply fibrous base material of claim 18, whereinthe non-linearly elastic fibers of the primary layer comprise lessfibrillated aramid fibers having a Canadian Standard Freeness of about525 or greater and the aramid fibers of the secondary layer comprisemore fibrillated aramid fibers having a Canadian Standard Freeness ofabout 525 or less.
 25. The two-ply fibrous base material of claim 18,wherein the secondary layer comprises, in percent by weight based on theweight of the secondary layer, about 10% carbon fibers, about 43% aramidfibers, about 30% filler material; about 15% carbon particles, graphiteor a mixture of carbon particles and graphite; and, about 2% novoloidfibers.
 26. The two-ply fibrous base material of claim 25, wherein thesecondary layer has about 15% carbon particles.
 27. The two-ply fibrousbase material of claim 18, wherein the novoloid fibers comprise about 1to about 10% fibers having an average length of about 3 mm and about 5to about 15% fibers having an average length of about 0.2 mm.
 28. Thetwo-ply fibrous base material of claim 18, wherein the secondary layercomprises about 2% cotton fibers.
 29. A non-asbestos friction materialcomprising a two-ply fibrous base material of claim 18 impregnated witha phenolic or modified phenolic resin, a silicone or modified siliconeresin, or a blend of a phenolic or modified phenolic resin with asilicone or modified silicone resins.
 30. The friction material of claim29, wherein the modified phenolic resin comprises an epoxy phenolicmodified resin.
 31. The friction material of claim 29, wherein thefriction material comprises about 30% to about 65% resin, by weight. 32.A friction material according to claim 29, comprising a clutch facing.33. A friction element according to claim 29, comprising a brake shoelining.
 34. A process for producing the two-ply fibrous base material ofclaim 18 comprising forming the primary layer and adhering the secondarylayer to the primary layer.
 35. A process for producing a non-asbestosfriction material comprising impregnating the two-ply fibrous basematerial of claim 34 with a phenolic or modified phenolic resin, asilicone or modified silicone resin, or a blend of a phenolic ormodified phenolic resin with a silicone or modified silicone resin andthereafter heating the impregnated two-ply fibrous base material to curethe resins.